The present invention relates to an ejector device of an injection molding machine, and in particular is one comprising a plurality of magnetic rod fixing means each of which is capable of fixing a portion or whole of each ejector rod to an ejector plate with magnetism of one or more permanent magnets in a detachable manner.
In the prior art, with an injection molding machine, dies (a fixed die and a movable die) are attached to a fixed platen and to a movable platen, and the movable platen is driven in directions to approach towards the fixed platen and to be withdrawn therefrom, and thereby closing and opening of the dies are performed. Synthetic resin in the molten state is supplied to a cavity within the dies that are closed together, and this synthetic resin in the molten state hardens so that a molded product is formed; and, after opening of the dies, this molded product is ejected from the movable die by an ejector device.
With an ejector device of an injection molding machine, an ejector plate is disposed at the rear side of the movable platen, one or a plurality of ejector pins (i.e. ejector rods) are inserted through the movable platen so as to slide freely therein, and the base end portions of these ejector pins are fixed to the ejector plate. By the ejector plate being driven in the directions to approach the platen and to be withdrawn therefrom, the ejector pins are driven forwards and backwards between eject positions in which they are advanced and wait positions in which they are retracted.
A construction is known (for example, refer to Patent Document #1) in which the ejector pins are made as single continuous unitary type pins, with the base end portions of these ejector pins being fixed to the ejector plate and with the ejector pins piercing through the ejector plate and a retainer plate being engaged to the ejector plate from its rear side by a plurality of bolts, so that base end flange portions of the ejector pins are sandwiched between the ejector plate and the retainer plate; and also a construction is known (for example, refer to Patent Document #2) in which the base end portions of the ejector pins are engaged to the ejector plate by being screwed thereinto.
And, with the ejector device of an injection molding machine described in Patent Document #3, an air cylinder is fixed to the ejector plate so as to face towards the platen, and base end flange portions of the ejector pin is linked via joint to the cylinder rod of the air cylinder. The base end flange portions of the ejector pin is engaged to concave portions of the joint in a manner so that their engagement can be released from the direction orthogonal to the axis, and is fixed by a bolt so as to rotate. The ejector pin can be exchanged by removing the bolt.
With regard to the ejector device of an injection molding machine described in Patent Document #4, each ejector pin include a tip end side ejector pin passing through a incorporated die that is assembled to the die, and a base end side ejector pin whose base end portion is fixed to the ejector plate, and the tip end side ejector pin is pressed and driven by the base end side ejector pin. In order to prevent operational faults due to thermal expansion of the embedded portion, the construction is adapted to permit some shifting of the tip end side ejector pin in directions orthogonal to the axis.    Patent Document #1: Japanese Laid-Open Patent Publication No. 5-245847;    Patent Document #2: Japanese Laid-Open Patent Publication No. 2000-301580;    Patent Document #3: Japanese Laid-Open Patent Publication No. 2007-98957;    Patent Document #4: Japanese Laid-Open Patent Publication No. 2005-254514.